The present invention relates to gas turbine engines, particularly to air flow distribution adjustment of gas turbine engines to ensure that low emissions not be affected by air flow cycle patterns of the engines whether the engine is designed as a simple air flow cycle or a heat-recuperated air flow cycle.
Industrial gas turbine engines are subject to increasingly stringent emission requirements. In order to provide a marketable power generation product, an engine producing the lowest possible emissions is crucial. Emissions of nitrogen oxides (NOx) and carbon monoxide (CO) must be minimized over specified engine operating ranges. To achieve this low level of emissions the combustion system requires the complete burning of fuel and air at low temperatures.
Combustors that achieve low NOx emissions without water injection are known as dry-low emissions (DLE) and offer the prospect of clean emissions combined with high engine efficiency. This technology relies on a high air content in the fuel/air mixture. While low emissions are critical, it is also important to minimize the cost of manufacturing and maintaining the combustion system, if a viable product is to be realized.
With regard to another aspect of the gas turbine engine, engine efficiency is always of critical concern. It is known that gas turbine efficiency can be substantially increased by recuperating heat from the engine exhaust. In a gas turbine engine using a heat-recuperating air flow cycle, compressor air is passed through a recuperator or heat exchanger attached to the engine exhaust end before entering the combustor. The resulting higher combustor inlet air temperature thus requires less fuel burn to achieve the same exit gas temperature compared with a gas turbine engine using a simple air flow cycle in which the compressor air enters the combustor directly and unaltered. The result of the heat-recuperated air flow cycle is significantly improved gas turbine cycle efficiency. The change in combustor inlet air temperature and result in a combustor fuel/air ratio shifting to achieve the same exhaust gas temperature. In low emission combustors the impact of fuel/air ratios shifting is the most severe because emission levels are intensely dependent on primary combustion zone fuel/air ratios. Adjusting the combustor geometry will compensate for the effect of fuel/air ratio change between combustors of gas turbine engines using simple and heat-recuperated air flow cycles. However, it can be cost prohibitive to adapt a gas turbine engine model which operates as a simple air flow cycle design, to be operable as a heat-recuperated air flow cycle design, or vice versa.
Therefore, there is a need to develop a method of engine design to cost effectively overcome the effect of the combustor fuel/air ratio changing between simple and recuperated air flow cycles when adapting a gas turbine engine model to be operable as either a simple or a heat-recuperated air flow cycle design while achieving low emission levels.
One object of the present invention is to provide a method of low emission engine design for cost effectively overcoming the effect of a combustor fuel/air ratio change between simple and recuperated air flow cycles of the combustor engine.
Another object of the present invention is to provide a method of combustor cycle air flow adjustment for a gas turbine engine to ensure that the flame temperature is maintained substantially the same whether the gas turbine engine utilizes a simple air flow cycle or a heat-recuperated air flow cycle.
A further object of the present invention is to provide an impingement cooling skin for a gas turbine engine combustor which serves dual purposes as a cooling device to cool the combustor wall and as a valve to adjust distribution of a total air mass flow between an air mass flow for combustion and an air mass flow for cooling, thereby changing the fuel/air ratio to ensure that the combustor flame temperature is maintained substantially the same whether the gas turbine engine operates as a simple air flow cycle engine or a heat-recuperated air flow cycle engine.
In accordance with one aspect of the present invention, a method of combustor cycle air flow adjustment for a gas turbine engine design is provided. The method comprises a step of changing a geometry of an air flow passage and thereby changing distribution of a total air mass flow between an air mass flow for combustion and an air mass flow for cooling, in order to ensure that a flame temperature in a primary combustion zone of a combustor is maintained substantially the same whether the gas turbine engine operates as a simple air flow cycle engine or a heat-recuperated air flow cycle engine.
The geometry of the air flow passage is preferably changed to decrease the air mass flow for combustion when the gas turbine engine uses a heat-recuperated air flow cycle, compared with the air mass flow for combustion when the gas turbine engine uses a simple air flow cycle. It is preferable that the changing of the air flow passage geometry is achieved by changing a geometry of an impingement skin of the combustor.
In accordance with another aspect of the present invention, an impingement cooling skin in combination with a gas turbine engine combustor is provided. The impingement cooling skin is attached to the combustor and comprises a first group of holes therein adjacent to a combustor wall section defining a primary combustion zone, the number and size of the holes of the first group being predetermined to substantially meet a cooling requirement for the combustor. The impingement cooling skin further includes a second group of holes therein adjacent to a combustor wall section defining a secondary combustion zone, the number and size of the holes of the secondary group being adjusted to substantially meet a flow distribution requirement whether the gas turbine engine operates as a simple air flow cycle engine or a heat-recuperated air flow cycle engine.
The present invention advantageously provides a cost effective solution to overcome the effect of combustor fuel/air ratio change between a simple air flow cycle and a heat-recuperated air flow cycle of the gas turbine engine operation. Without any added parts, the impingement cooling skin of the combustor, according to the present invention, serves dual purposes as a cooling device to cool the combustor wall and as a valve to adjust the distribution of the total air mass flow between the air mass flow for combustion and the air mass flow for cooling such that the required air mass flow for maintaining the combustor flame temperature substantially the same, is achieved regardless of the engine air flow cycle pattern. Thus, low emissions of the gas turbine engine are ensured.
Other advantages and features of the present invention will be better understood with reference to a preferred embodiment described hereinafter.